The cardiovascular system is resulated by the central nervous system via the sympathetic presanslionic nerves (SPN). The function of the SPN depends upon its morphology and connections. To elucidate these properties, four specific hypothesis are tested using state-of-the-art neuroanatomical and neurophysiolosical techniques. Hypothesis #1 - Sympathetic communications white rami receive innervation form multiple spinal levels. Cell bodies of orisin of different white rami will be located using the retrosrade transport of horseradish peroxidase(HRP) and by stimulating different segmental levels of the spinal cord while recording from various white communicating rami. Hypothesis #2 - SPN axons branch in the spinal cord to exit via different ventral roots and innervate different sanglia. Axon branching will be detected using the multiple-label retrograde transport technique and by antidromic activation of a SPN cell body by stimulating different white rami. Hypothesis #3 - The ultrastructure of SPN and the location of its afferent endings are important determinants of SPN function. Combining HRP and electronmicroscopic techniques, the morphology of SPN, its boutons and its afferent interneurons will be quantitatively characterized. Terminations of spinal and supraspinal inputs to the SPN will be traced by location of degenerating boutons. Cell body properties and axon conduction velocities will be compared to cell morphology using intracellular recordings and intracellular HRP injection. Hypotehsis #4 - Descending spinal sympathetic pathways are organized in a "viscerotopic" manner. After physiologically locating SPN cell bodies, the organization of brain stem and hypothalamic connections will be detected using retrograde transport techniques after localized microinjections. Also specific brain stem loci will be electrically stimulated while recording from various sympathetic rami to demonstrate laminar organization.